gh-87092: expose the compiler's codegen to python for unit tests (GH-99111)

Lib/test/test_compiler_codegen.py

@@ -0,0 +1,50 @@
+
+from test.support.bytecode_helper import CodegenTestCase
+
+# Tests for the code-generation stage of the compiler.
+# Examine the un-optimized code generated from the AST.
+
+class IsolatedCodeGenTests(CodegenTestCase):
+
+    def codegen_test(self, snippet, expected_insts):
+        import ast
+        a = ast.parse(snippet, "my_file.py", "exec");
+        insts = self.generate_code(a)
+        self.assertInstructionsMatch(insts, expected_insts)
+
+    def test_if_expression(self):
+        snippet = "42 if True else 24"
+        false_lbl = self.Label()
+        expected = [
+            ('RESUME', 0, 0),
+            ('LOAD_CONST', 0, 1),
+            ('POP_JUMP_IF_FALSE', false_lbl := self.Label(), 1),
+            ('LOAD_CONST', 1, 1),
+            ('JUMP', exit_lbl := self.Label()),
+            false_lbl,
+            ('LOAD_CONST', 2, 1),
+            exit_lbl,
+            ('POP_TOP', None),
+        ]
+        self.codegen_test(snippet, expected)
+
+    def test_for_loop(self):
+        snippet = "for x in l:\n\tprint(x)"
+        false_lbl = self.Label()
+        expected = [
+            ('RESUME', 0, 0),
+            ('LOAD_NAME', 0, 1),
+            ('GET_ITER', None, 1),
+            loop_lbl := self.Label(),
+            ('FOR_ITER', exit_lbl := self.Label(), 1),
+            ('STORE_NAME', None, 1),
+            ('PUSH_NULL', None, 2),
+            ('LOAD_NAME', None, 2),
+            ('LOAD_NAME', None, 2),
+            ('CALL', None, 2),
+            ('POP_TOP', None),
+            ('JUMP', loop_lbl),
+            exit_lbl,
+            ('END_FOR', None),
+        ]
+        self.codegen_test(snippet, expected)